/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing,
 * software distributed under the License is distributed on an
 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
 * KIND, either express or implied.  See the License for the
 * specific language governing permissions and limitations
 * under the License.
 */

package org.apache.iotdb.db.trigger.service;

import org.apache.iotdb.commons.file.SystemFileFactory;
import org.apache.iotdb.db.conf.IoTDBConfig;
import org.apache.iotdb.db.conf.IoTDBDescriptor;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import java.io.IOException;

public class TriggerClassLoaderManager {
    private static final Logger LOGGER = LoggerFactory.getLogger(TriggerClassLoaderManager.class);

    private static final IoTDBConfig CONFIG = IoTDBDescriptor.getInstance().getConfig();

    /**
     * The dir that stores jar files.
     */
    private final String libRoot;

    /**
     * activeClassLoader is used to load all classes under libRoot. libRoot may be updated before the
     * user executes CREATE TRIGGER or after the user executes DROP TRIGGER. Therefore, we need to
     * continuously maintain the activeClassLoader so that the classes it loads are always up-to-date.
     */
    private volatile TriggerClassLoader activeClassLoader;

    private TriggerClassLoaderManager(String libRoot) throws IOException {
        this.libRoot = libRoot;
        LOGGER.info("Trigger lib root: {}", libRoot);
        activeClassLoader = new TriggerClassLoader(libRoot);
    }

    /**
     * Call this method to get up-to-date ClassLoader before registering triggers
     */
    public TriggerClassLoader updateAndGetActiveClassLoader() throws IOException {
        TriggerClassLoader deprecatedClassLoader = activeClassLoader;
        activeClassLoader = new TriggerClassLoader(libRoot);
        deprecatedClassLoader.close();
        return activeClassLoader;
    }

    public TriggerClassLoader getActiveClassLoader() {
        return activeClassLoader;
    }

    /////////////////////////////////////////////////////////////////////////////////////////////////
    // singleton instance holder
    /////////////////////////////////////////////////////////////////////////////////////////////////

    private static class TriggerClassLoaderManagerHolder {
        private static final TriggerClassLoaderManager INSTANCE;

        static {
            try {
                SystemFileFactory.INSTANCE.makeDirIfNecessary(CONFIG.getTriggerDir());
                INSTANCE = new TriggerClassLoaderManager(CONFIG.getTriggerDir());
            } catch (IOException e) {
                throw new RuntimeException(e);
            }
        }
    }

    public static TriggerClassLoaderManager getInstance() {
        return TriggerClassLoaderManagerHolder.INSTANCE;
    }
}
